The present invention relates to a video signal monitoring apparatus and, more particularly, to an apparatus for monitoring a Y/color difference component signal.
Video signals are prescribed in various formats, e.g., the RGB component signal format, the Y/color difference component signal format and the NTSC composite signal format. In conventional video systems, the input-side video signal format (RGB component signal) is the same as the output-side video signal format (RGB component signal). More specifically, in a conventional video system, an RGB component signal is input from an input device (e.g., a camera) and is converted into a Y/color difference component signal to be transmitted. Thereafter, in the video system, the Y/color difference component signal is again converted into an RGB component signal, which is output through an output device (e.g., a television set). The RGB component signal on the output side (display side) is theoretically the same as that on the input side and has no abnormal value, as long as no problem occurs with the transmission system and devices constituting the video system.
In some cases, as a result of the recent development of computer graphic apparatuses, an input device handling a Y/color difference component-signal (e.g., a computer) is used instead of an input device handling an RGB component signal (e.g., a camera). Also, with the development of editing devices in recent years, it has become possible to adjust a Y/color difference component signal according to one's intention by using an editing device in a transmission stage.
FIG. 1 shows the gamut of an RGB component signal and the gamut of a Y/color difference component signal. As shown in FIG. 1, the gamut of a Y/color difference component signal is wider than that of an RGB component signal. Therefore, in a case where a Y/color difference component signal is used as an input-side video signal format or in a case where the level of a Y/color difference component signal is adjusted according to one's intention in a transmission stage, an RGB component signal on the output side (display side) may have an abnormal value not existing in the gamut on the output side. In such a case, therefore, there is a need to monitor whether or not the RGB component signal on the output side (display side) has an abnormal value.
A method of monitoring an RGB component signal on the output side (display side), e.g., one described in patent document 1 shown below is known.
(Patent Document 1)
Japanese Patent Publication No. 4-77518 (FIG. 1)
In the method described in patent document 1, a Y/color difference component signal is converted into an RGB component signal and determination is made as to whether or not any converted RGB value exists in the gamut on the output side as a normal value. This method enables checking of a gamut error in the converted RGB component signal but has a problem in that it is difficult to grasp how a gamut error is caused from the original Y/color difference component signal. In a case where a gamut error in the RGB component signal is detected, it is difficult for an operator to grasp how to adjust the ordinal Y/color difference component signal in order to correct the gamut error.